Adsorption of hydrogen on the Pd(1 0 0)-p(2 × 2)-p4g-Pd3Ti surface

Ti/Pd(1 0 0) surface alloy has p(2 × 2)-p4g symmetry. Hydrogen adsorption removes the lateral distortion of the first layer atoms to yield c(2 × 2). We studied the hydrogen adsorption by thermal desorption experiment and self-consistent total-energy calculation based on density-functional theory. Thermal desorption spectra of hydrogen from this surface are composed of two components: a relatively broad peak shifting from 355 to 345 K with increasing coverage and a sharp desorption peak at 380 K. The former is assigned to hydrogen desorption occurring on the c(2 × 2) domains. The shape and peak temperature of the latter is similar to the sharp hydrogen desorption peaks reported on the p(2 × 2)-p4g surfaces of Al/Pd(1 0 0) and H/Cu(1 0 0). It is suggested that the sharp desorption peak may be intrinsic to hydrogen desorption from the p(2 × 2)-p4g surfaces. The nature of the hydrogen adsorption site is discussed.